The present invention relates to controls for household appliances and, in particular, to a water height control for washing machines providing improved water efficiency for standard washing machines.
Conventional clothes washing machines provide for a tub for receiving clothing, water, and detergent and for providing agitation to clean clothing. The amount of water in the tub is typically controlled by a selector switch on the washing machine console. An electric valve is controlled to allow the tub to fill until a desired water level is sensed.
A well-established method of sensing the water level in the tub employs a pressure dome communicating with the tub to receive water from the tub into the dome. As the water rises, the pressure of trapped air in the dome increases. A mechanical pressure switch is attached to the dome to switch when a particular air-pressure has been reached.
The pressure switch used for this purpose typically provides a diaphragm working against a spring. The diaphragm is connected to a set of contacts that close or open when the diaphragm has been displaced by air pressure to a predetermined amount. The spring against which the diaphragm works may be preloaded by a cam that may be rotated by the user to adjust the desired water level setting. This mechanical pressure switch provides essentially a two state or binary pressure output.
High-end washing machines may provide for more sophisticated water management using a microprocessor control system handling all the functions of controlling the washing machine in addition to specialized cycles beyond those normally provided by a mechanical timer, such as multilevel temperature control (for example to optimize enzymatic action), directed detergent/bleach/softener injection, additional user signals (for example indicating that a garment may be added after the beginning of a cycle), delayed washing, child lockout, and improved water level control.
This latter feature of improved water level control can match the amount of water used to the size of the load saving as much as 23 gallons of water per load. This is done by using a solid-state pressure sensor that delivers a range of water level signals (rather than a switched binary signal per the mechanical pressure switch of the prior art) and a flow meter measuring the amount of water flowing into the tub. By determining the height of the water (through the pressure sensor) and the amount of water, the size of the load may be deduced and the proper total amount of water determined. Such sophisticated control is normally implemented through the use of a central control circuit board supporting a microprocessor and related control circuitry.
Improved control of water usage to match the size of the load being washed can have a significant environmental benefit but this feature is not normally available on lower end washing machines which do not require the range of features justifying full microprocessor control and which may be designed instead to employ a mechanical pressure switch and a mechanical cycle timer.